The series -- based on the 1992 feature of the same name -- was a hit for the WB Network before moving to UPN two seasons ago. Ratings have never been spectacular, but the show's fans have been fiercely loyal.
In an interview promoting the upcoming series finale, Whedon acknowledged that ratings have always been problematic, but he took satisfaction in knowing that his creation has achieved a place of prominence in contemporary culture.
"Our viewership has never been as large as the awareness of us," said Whedon. "That's just the way it is, and that doesn't bother me. Buffy was designed to be a pop culture icon. She became that, and so she exists beyond her ratings."
For the uninitiated, Buffy Summers -- played by Sarah Michelle Gellar -- is a teenage girl who discovers that her mission in life is to do battle with vampires. Over the course of the show, Buffy and her friends have done business with all sorts of supernatural evils.
The final episode pits Buffy against her evil opponent ever, Caleb -- played by Nathan Fillion. At stake is nothing less than whether good or evil will reign on Earth.
Whedon wasn't saying how the story will end. But he has made his peace with the idea that people would be able to find out about it at any number of Web sites devoted to the show -- and there's nothing he can do to stop leaks from getting out.
"I gave up (trying) about a year and half ago," he said. "Even if you use alternative endings, you have to put the real ending on some time, and people will see it."
But Whedon said there are lots of fans who would avoid looking for "spoilers" -- the term given to premature leaks about story lines and endings.
"There are people who want to see it pure," he said.
That group would include Marti Noxon -- one of the show's producers -- who said she was unhappy when she inadvertently read a spoiler about the final episode of "The Sopranos" last season. Still, Noxon said she appreciates the intense fan interest in the show.
"We have some fairly rabid fans, but their love is what keeps us strong," she said. "I feel like a lot of the fans feel like the show is theirs, and it is."
Noxon said she owes her career to the show.
"I was still working as an assistant when I got this job," she said. "I went from being a non-entity to having a career. Joss challenged me from the beginning. His goal was to make us all better."
Noxon said everybody at the show knows it's possible they might someday be curiosities at "Buffy" fan conventions.
"In our best days, we all hope that it's the show of shows," she said. "We're all hoping we didn't just 'peak in high school.'"
Whedon said the series finale is not necessarily the end of "Buffy." He said "the door is open" for future "Buffy" projects, possibly including a feature.
But he said no matter what happens from here, "Buffy" has accomplished its mission -- to validate the idea that a young girl can wield such enormous power.
"It has changed attitudes about heroines and what boys will watch," he said. "That's a more important legacy to me."
Whedon said the series finale deals "very specifically with how she decides to use that power" -- but he offered only a general idea of how the "Buffy" adventure ends.
"We do not destroy the fabric of the entire universe," he said, "and some people live."